On Tue, Mar 18, 2014 at 04:38:25PM +0100, Arnd Bergmann wrote: > On Tuesday 18 March 2014 20:54:44 Vinod Koul wrote: > > On Mon, Mar 17, 2014 at 03:37:47PM -0400, Santosh Shilimkar wrote: > > > >> To simplify this bit more, you can think of this as DMA channels, flows > > > >> are allocated and DMA channels are enabled by DMA engine and they remains > > > >> enabled always as long as the channel in use. Enablling dma channel > > > >> actually don't start the DMA transfer but just sets up the connection/pipe > > > >> with peripheral and memory and vice a versa. > > > >> > > > >> All the descriptor management, triggering, sending completion interrupt or > > > >> hardware signal to DMAEngine all managed by centralised QMSS. > > > >> > > > >> Actual copy of data is still done by DMA hardware but its completely > > > >> transparent to software. DMAEngine hardware takes care of that in the > > > >> backyard. > > > > So you will use the dmaengine just for setting up the controller. Not for actual > > > > transfers. Those would be governed by the QMSS, right? > > > > > > > Correct. > > > > > > > This means that someone expecting to use dmaengine API will get confused about > > > > this and doing part (alloc) thru dmaengine and rest (transfers) using some other > > > > API. This brings to me the design approach, does it really make sense creating > > > > dmaengine driver for this when we are not fully complying to the API > > > > > > > Thats fair. The rationale behind usage of DMEngine was that its the closest > > > available subsystem which can be leveraged for this hardware. We can > > > pretty much use all the standard DMAEngine device tree parsing as well as > > > the config API to setup DMAs. > > > > > > I think you made your stand clear, just to confirm, you don't prefer this > > > driver to be a DMAEngine driver considering it doesn't fully complying to > > > the APIs. We could document the deviation of 'transfer' handling to avoid > > > any confusion. > > Yup, a user will just get confused as the driver doenst conform the dmaengine > > API. Unless someone comes up witha strong argument on why it should be > > dmaengine driver and what befits we see form such a model, i would like a > > damengine driver to comply to standard API and usage. > > I think it would be possible to turn the QMSS driver into a library and have > the packet DMA code use the proper dmaengine API by calling into that code. > > The main user of packet DMA (the ethernet driver) would however still have > to call into QMSS directly, so I'm not sure if it's worth the effort. Wouldn't that make clients use a standard API and also help in transaction management by using existing infrastructure -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
